Devices for ensuring an electric contact between rotary parts of an electric machine



SCHWAB ETAL DEVICES FOR ENSURING AN ELECTRIC CONTACT July 29, 1958 B.

BETWEEN ROTARY PARTS OF AN ELECTRIC MACHINE Filed March 16, 1956 United States Patent O DEVICES FOR ENSURING AN ELECTRIC CON- TACT BETWEEN ROTARY PARTS OF AN ELECTRIC MACHINE Bernard Schwab, Asnieres, and Louis Vautrey, Fontenayaux-Roses, France, assignors to the Commissariat a lEnergie Atomique, Paris (Seine), France, a state administration Application March 16, 1956, Serial No. 571,989

Claims priority, application France March 30, 1955 3 Claims. (Cl. 310-178) The present invention relates to devices for ensuring an electric contact between rotary parts of an electric machine, in particular between a fixed element and an element rotating about said fixed element, this contact being obtained by means of mercury or any other metal in the liquid or molten state. Our invention is more especially but not exclusively concerned with homopolar generators (of the Poirson type) intended to supply electric current for instance with an intensity ranging from 10,000 to 20,000 amperes under a voltage of some tenths of a volt.

- The chief object of our invention is to provide a device of this kind which is better adapted to meet the requirements of practice than those used up to the present time, especially concerning the cooling of the conductor liquid.

The essential feature of our invention consists in making use of the centrifugal force for causing the conductor liquid to flow in a continuous fashion through a circuit a portion of which is external to the machine and includes liquid cooling means.

Other features of our invention will become apparent in the course of the following detailed description of one specific embodiment thereof, with reference to the accompanying drawings, given merely by way of example and in which:

Fig. 1 is an axial sectional view of a homopolar generator made according to our invention.

Fig. 2 is a diagrammatical view of the liquid circuit used in said generator.

Fig. 3 shows, on an enlarged scale and with parts in section, a portion of the brushes of the generator.

Homopolar generators have been known for some time, the essential elements of such generators being a metal shaft or cylinder rotating in a magnetic field (see for instance Y. Rocard, Electricit, page 208, Masson & 00., Paris), in such manner as to be able to supply between at least two points of said shaft a current of high intensity under a low potential difference.

Such generators, also called Poirson generators, have been little used up to this time although they are of great interest in some applications which require very high intensities. This is for instance the case for welding machines, for electrolysis, for magnetic fields of high intensity used in particle accelerators, and also for electro-rnagnetic pumps, such as used for circulating through a conduit a metal in the liquid form, in installations for evacuating an intensive amount of calories (by means of sodium or by means of the eutectic mixture of sodium and potassium in the liquid state, etc.).

But such generators, as they were made up to the present time, involved very serious drawbacks concerning the collector brushes which quickly became out of use and created important losses. It has been proposed to make use of liquid brushes but, up to the present time, no satisfactory results were obtained.

Patented July 29, 1958 In order to obviate these drawbacks, we proceed in such manner, according to the present invention, that the current is collected by means of a liquid (mercury, sodium-potassium, etc.) forming at least one brush and subjected, by the action of the centrifugal force developed by the rotation of the shaft or rotor, to a circulation making it possible to provide for its cooling.

Of course, such an arrangement according to our invention may be used for various kinds of machines other than the homopolar generators above referred to.

On Fig. 1, we have shown, merely by way of example, a homopolar generator provided with two liquid brushes arranged according to the present invention, this generator including two magnetic systems and two liquid brush systems cooperating with the same shaft. It must be well understood that we might use a single magnetic field, and possibly a single liquid brush system, forming one terminal, whereas the other one might be disposed directly at the end of the shaft or be constituted by the metal mass of the machine.

In the embodiment illustrated by the drawings, the generator includes a shaft 1, for instance a vertical shaft, the lower half of which cooperates with a magnetic circuit and the upper half of which cooperates with another magnetic circuit, said shaft being driven at 2.

The magnetic systems include for instance windings 3, 4 cooperating respectively with the two magnetic circuits including:

The first one (upper magnetic circuit), a disc-shaped member 5, the upper half of shaft 1, and the elements 6, 7 of a casing,

The other one (lower magnetic circuit), a member 3 analogous to member 5 and insulated therefrom, the lower half of shaft 1, and the elements 9, 10 of the lower frame.

Brushes are provided on the shaft, opposite chambers 11, 12 formed inside said casing and said frame. Said brushes include the following elements:

a. Two movable annular elements 13, of triangular radial section, mounted on shaft 1 and which may be connected together by bolts 41 which apply them against a sleeve 14 fitted on the shaft;

b. Fixed annular elements surrounding elements 13 and located at a small distance therefrom so as to leave an annular interval 15 sufiicient for the passage of mercury; said fixed elements may be two elements 16, 17 held together by bolts 18; and

c. Mercury located in said annular interval 15.

We will now describe only one of these systems 13, 15, 16, 17, 18, since both of them are practically identical.

The lower fixed element 16 is provided with a circular groove 19 the filling of which when the machine is being started permits of supplying a sutficient amount of mercury for the operation. The side of this groove turned toward shaft 1 is preferably limited by an edge 20 (Fig. 3) which projects into a corresponding groove 21 of the movable element 13, so as to prevent losses of mercury toward the interval between the shaft and the stator.

The inflow of liquid into annular interval 15 is obtained as follows: on the one hand, at the top portion of the upper elements 17, by passages 22 fed through conduits 23 disposed in radial planes at to each other about the axis of shaft 1; and on the other hand, at the bottom partof the lower piece 16, by passages 24 opening into groove 19 and supplied through respective conduits 25.

The outflow of liquid from annular passage 15 is obtained by providing at the periphery of every movable element 13, between said element and the fixed elements 16, 17, a circular conduit such as 26 from which start- 3 several outflow conduits 27 connected with conduit 26 through passages 28.

Of course, elements 13, 16 and 17 are made of metals capable of resisting, at the maximum temperature of utilization, the action of mercury or another metal used but which are perfectly wetted by mercury or said other metal, in order to reduce contact resistances which might cause supplementary losses.

Said elements 13, 16 and 17 are for instance made of electrolytic copper, in the case where the liquid is mercury or the sodium-potassium eutectic mixture. The remainder of the circuit may advantageously be made of stainless steel.

Externally of the machine, the feed conduits 23, 25 and the outflow conduits27 are connected with a heatinterchanger device 29 (Fig. 2), with the interposition of any devices for adjusting the flow rate, such as valves 45, and for measuring said flow rate, such as flowmeters 30. Of course, the circuits of the two brushes mounted on shaft 1 are independent.

The means for collecting current from the brushes of the machine are suitably arranged in the central portion in the form of discs or bars 31, 32. The connection between the two respective brushes and said collecting bars is advantageously obtained by two series of copper bars 33 disposed parallel to the axis in the form of a squirrel cage.

The arrangement of such copper bars in squirrel cage fashion constitutes another characteristic of the invention, which is to compensate for the armature reaction.

Preferably, the chambers 11 and 12 of the generator are perfectly gas-tight and filled with a neutral atmosphere (for instance of nitrogen). However, it seems advantageous to house windings 3, 4 in chambers 34 separate from said chambers 11 and 12 so as to permit, if necessary, of cooling the windings by forced draft.

The operation of such a machine is that of known homopolar generators, but with the supplementary feature that the brushes are of the liquid type and that the liquid used for said brushes is caused to circulate constantly and to pass through the heat-interchangers which keep its temperature below a suitable maximum.

Advantageously, the liquid conduits should be emptied during the periods where the machine is not in operation, means being then provided to permit of quickly filling the liquid circuit when the machine is to be restarted.

Fig. 2 shows a system which may be used for this purpose (only the circuit relating to one of the two liquid brushes has been shown).

' A tank 35 (which may be common to the two liquid brushes) is provided in the lower portion of the machine so that the liquid circuit may be emptied, when so desired, merely by opening valves such as 36 and placing said tank under atmospheric pressure.

' border to fill the liquid circuits, the tank is placed under pressure, for instance by sending nitrogen at 42, in particular through the conduit 37 which feeds chambers 11 or 12 at 38. This pressure causes liquid to rise in a tube such as 39, so that, through a pipe 40, it reaches the feed conduits 23, 25. The liquid tends to fill groove 19. If the machine is then started, the liquid is gradually projected in the centrifugal direction. The reserve formed in groove 19 ensures a regular filling of the annular interval, liquid being continuously supplied through pipe 40. Finally a time comes when the whole of the circuit is filled with liquid, which is indicated by the maximum pressure given by pressure gauge 44, and the liquid flows in a closed circuit and through the heat-interchanger 29. Valve 36 is then closed for the whole time the machine is to be operated.

In a general manner, while we have, in the above description, disclosed what We deem to be practical and eflicient embodiments of our invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement,

disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What we claim is:

1. In an electric machine including a fixed frame and a shaft rotatable in said frame about a given axis, a device for ensuring an electric contact between said parts which comprises, in combination, an annular member rigid with said shaft, the section of said member by any radial plane passing through said axis being a triangle, the base of said triangle being along the wall of said shaft and its apex being at a greater distance from said axis than said base, an annular member rigid with said frame, the section of said last mentioned member by any radial plane passing through said axis including two lines at least substantially parallel to, and at a small distance from, the sides of said triangle meeting at said apex, respectively, whereby an annular interval is left between said two members, the general form of said interval being that of two frusto-conical elements opposed by their larger bases which coincide with each other along a common' circle, means forming a conductor liquid circulation circuit including a portion external to said machine and a portion constituted by said annular interval, one end of said external circuit portion being in communication with the smaller bases of said frusto-conical interval elements and the other end of said external circuit portion being in communication with the part of said annular interval extending along said common circle, whereby liquid in said circuit is caused by centrifugal force to flow from said smaller bases toward said common circle, thus producing circulation through said circuit, and liquid cooling means in said liquid circulation circuit external portion;

2. In an electric machine including a fixed frame and a shaft rotatable in said frame about a given axis, a device for ensuring an electric contact between said parts which'comprises in combination, an annular member rigid with said shaft the outer wall of said annular memher being a body of revolution about said axis, the generatrix of said body between two planes perpendicular to said axis being constituted by two lines each starting froma p'Oint located in one of said planes respectively,

said points being located at least approximately at the same distance from said axis, both of said lines ending at a third point located in a third plane parallel to and intermediate between said two planes, said third point being at a distance from said axis greater than said above mentioned distance, an annular member rigid with said frame coaxially surrounding said first mentioned member, the inner wall of said second mentioned member being a body of revolution about said axis, the generatrix of said last mentioned body between said two planes being constituted by two lines parallel and close to said two above mentioned lines respectively, whereby, between said two first mentioned planes, an annular interval is left between said two members, said annular interval having two portions of substantially the same diameter located in said two first mentioned planes respectively, and a portion of greater diameter located in said third mentioned plane, means forming a conductor liquid circulation circuit including a section external to said machine and a section constituted by said annular interval, one end of said external circuit section being in communication with both said portion of smaller diameter of said annular interval and the other end of said external circuit section being in communication with said portion of greater diameter of said annular interval, whereby liquid is caused by centrifugal force to flow through said annular interval from said portions thereof of smaller diameter to said portion thereof of greater diameter, thus producing circulation through said circuit without requiring a pump for this purpose.

3. In an electric machine according to claim 2 where said shaft axis is vertical, so that said portions of'smaller' diameter of said annular interval are located one above the other, said second mentioned member being provided with an annular groove opening upwardly opposite that of said portions of smaller diameter located at the lower level, and an annular baflle carried by said second mentioned member along the inner edge of said groove, said ridge extending upwardly above the level of said last mentioned portion of smaller diameter of said annular interval, so as to prevent overflow of liquid from said groove.

References Cited in the file of this patent UNITED STATES PATENTS 1,443,644 Nobuhara Jan. 30, 1923 6 Gill Sept. 9, 1924 Kobel May 28, 1946 Lessmann Mar. 21, 1950 Barnes Mar. 11, 1952 Watt July 3, 1956 Sellers Mar. 19, 1957 FOREIGN PATENTS France Sept. 25, 1928 

